That ... may be required (ina ... ekzhthqh). Divinely ordered sequence, first aorist passive subjunctive of ekzhtew, a late and rare verb outside of LXX and N.T., requiring as a debt the blood of the prophets. Which was shed (to ekkecumenon). Perfect passive participle of ekcew and ekcunnw (an Aeolic form appearing in the margin of Westcott and Hort here, ekcunnomenon, present passive participle). If the present passive is accepted, it means the blood which is perpetually shed from time to time. From the foundation of the world (apo katabolh kosmou). See also Matthew 25:34 ; John 17:24 ; Ephesians 1:4 , etc. It is a bold metaphor for the purpose of God.